This invention relates to improvements in or relating to multi-layer bearings.
One type of multi-layer bearing known in the art is disclosed in Japanese Patent Application Laid-Open No. 45440/79, for example. This multi-layer bearing will be described as an example to show the state of the art. The multi-layer bearing comprises a metal backing layer, and a porous material layer lined with the aforesaid metal backing layer, the porous material layer being impregnated in its interior and coated on its surface with a composition containing, by weight, 5-40% tetrafluoroethylenehexafluoropropylene copolymer resin (hereinafter FEP) and the balance being (60-95%) essentially polytetrafluoroethylene (hereinafter PTFE). The multi-layer bearing of this construction of the prior art has been found rather unsatisfactory in anti-cavitation, wear resistance and low friction characteristics which are very important characteristics for plain bearings. The anti-cavitation characteristic represents the property which, when separation of gas or production of vapor occurs in the lubricant and the gas or vapor vigorously exerts impact force on the sliding surface or end surface of the bearing, enables the sliding surface and end surface of the bearing to be free from damage, including wear, peeling and cracking, that might otherwise be caused. As subsequently to be described, a cavitation tester is used for determining the anti-cavitation characteristic of a bearing by measuring a loss of volume of the sliding surface or end surface of the bearing.